Current technology for detecting and mapping buried acoustic sources often involves the manual placement of physical accelerometers or microphones, and careful ambient noise reduction in order to hear the weak acoustic sound emanating from a buried or underground source. The source may be human or that due to physical structural changes underground.
In the past, single Laser Doppler Velocimetry (LDV) or Laser Vibrometry systems have been used to measure the acoustic vibration/sound of a distant target. An example is the use of a laser beam bounced off of a distant window pane used to hear the conversations on the other side of the window. In this case, the LDV system acts as a remote, non-contact, microphone.
Also, in the past, locating an underground passive object has been conducted using reflected acoustic pulses (produced by an explosive charge) and detecting the time-delayed acoustic signals using three or more acoustic microphones placed at several remote (moderate distances) locations from the explosive charge. This technique is often used in geology to locate and map underground oil reserves or structures. The location of the underground structures is determined by cross-correlation of the time-delayed microphone signals and triangulation in three dimensions of the acoustic emanating signals. A similar triangulation technique is used in seismology to locate the position of earthquakes sensed by several seismic recorders located around the globe.
There remains a need in the art for a system and method for locating an underground acoustic source using multiple LDV beams and triangulation of the cross-correlated acoustic signals.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified need could be fulfilled.